A mammary‐derived growth inhibitor (MDGI) related 70 kDa antigen identified in nuclei of mammary epithelial cells

Publisher Website
Google Scholar
Abstract
The aim of the present study was to investigate the expression of the mammary derived growth inhibitor (MDGI) and the subcellular localization of MDGI related antigens in bovine mammary glands. Cell‐free translation of poly (A+) = RNA, immunoprecipitation with rabbit anti‐MDGI‐antibodies, and estimation of the relative contents of MDGI by a radioimmunoassay in mammary tissue of different functional statess revealed that the 13 kDa MDGI was dramatically increased in terminally differentiated mammary tissue compared with the proliferating tissue from pregnant animals. To address the question of tissue localizationl, polyclonal anti‐MDGI antibodies and antibodies directed aganist a sythetic peptide corresponding ot residues 69 to 78 of MDGI were used. Western blotting of tissue fractions revealed the cytosolic and microsomal localization of MDGI. Additionally, both types of antibodies a 70‐kDa antigeninthe unclear fractionof differentiated mammary glands. Salt extraction and DNase I digestion of isolated unclei, as well as chromatin purification, indicated an association of the 70‐kDa antigen with the chromatin. By means of the immunogold technique, MDGI‐related antigens were localized within euchromatic unclear regions of epithelial cells in the intact differentiated mammary gland. The immunostaining was markedly diminished in the proliferating tissue. This finding raises the possibility that MDGI and the 70‐kDa antigen influence cell proliferation by acting on geneexpression within the unclei of mammary glands.